present invention refers to a method of manufacturing plastic panels, preferably of thermoplastic resin, which are provided on at least one side with undercut protrusions developed integral with them, the panel blank being shaped by extrusion from a slot nozzle and then conducted through at least one roll nip, one roll of which is provided with recesses corresponding to the projections.
Nub panels of plastic are used, in particular, in the construction of concrete containers when it is desired to construct liquid-tight as well as gas-tight chemically-resistant containers. The plastic panels form the lining of such containers. They produce resistance to chemicals and liquids. The mechanical strength of the overall construction is obtained essentially from the concrete construction. In addition, nub panels of plastic may also be used for the external walls of concrete structures such as in the construction of concrete walls, piles, docks, bridges and the like which are exposed to the elements, such as salt water. Difficulties generally exist in attaching the plastic panels to the concrete structure since the smooth plastic panel does not form a firm mechanical attachment to the concrete. The use of adhesives does not lead to satisfactory results over the long term.
For this reason, various anchoring elements with undercuts have been proposed which are arranged on one side of the plastic panel and are included in the concrete upon the production of the container. In this way, although the desired firm attachment between plastic panel and concrete understructure is obtained, the arranging of the known anchoring elements on the plastic panels is, however, comparatively expensive since it is effected subsequently and requires several operating steps.
Thus, for instance, a method is known from Federal Republic of Germany OS 31 08 972 in which separately produced anchor nubs are placed simultaneously on the plastic panel and fastened to it by welding. This type of application of anchoring nubs is extremely time-consuming in view of the large number of anchoring elements to be applied, or else a correspondingly expensive apparatus is needed. In addition, in the region of their base, these anchoring nubs have sharp-edged transitions in themselves and with respect to the plastic panel, as a result of which notch stresses result with the well-known overstressing.
From French Patent 11 02 294 a method is known by which lining panels are produced by extrusion. Upon the extrusion, anchoring ledges are provided on one side of the panel, determined by the extrusion process, over the entire length of the panel, which ledges may be also undercut. This method can be used only for relatively thick plastic panels in order to assure a uniform development of the anchoring strips. The latter also result in a linear removal of force between the plastic panels and the concrete of the structure. This results in a non-uniform course of the stress in the panel, which reduces its long-time resistance.
Finally, European Patent Application 294 507 describes a method of extruding nub panels in which the nubs of the plastic panel which are produced on a calender must, however, furthermore be conducted through cutting device in order to produce the undercuts which are subsequently to fasten the nub panel in the concrete container. The nub panels produced in this manner are not able to cover all cases of need due to their merely relatively limitedly possible undercuts. Furthermore, the additional operation of the application of the undercuts increases the cost. In addition, special measures must be taken for the removing and collecting of the plastic parts which have been cut off.